Wide band traveling wave antenna



N. E. LINDENBLAD 2,293,753 WIDE BAND TRAVELING WAVE ANTENNA Filed Aprill0, 1941 2 Sheets-Sheet l 70/5 LecZZ'on 1 l0 1/ l2 flnZ/vza, lenqzh in,Waredenqfiw INVENTOR ATTORNEY Patented Aug. 25, 1942 WIDE BAND TRAVELINGWAVE ANTENNA Nils E. Lindenblad, Rocky Point, N. Y., assignor to RadioCorporation of America, a corporation of Delaware Application April 10,1941, Serial No. 387,830

18 Claims.

The present invention relates to multiple wavelength traveling waveradiators and, more particularly, to such radiators designed to cover awide frequency band.

An object of the present invention is the provision of a radiator havinga constant resistive input over a wide frequency spectrum.

Another object is to provide a traveling wave antenna which has a lowfactor of reflection over a wide frequency band.

Still another object of the present invention is the provision of a wideband short wave antenna suitable for producing energy concentration foreither beam or broadcasting services.

In order to accomplish the above mentioned objects, and others which mayappear from the following detailed description, in accordance with theprinciples of the present invention I propose to provide a radiatorhaving a maximum diameter which is a large fraction of the length of theoperating wave and which is several operating wavelengths in length. Theradiator is gradually tapered at the end to which the transmission lineis connected to the diameter of the transmission line conductor so as toprovide a smooth transfer of energy from the transmission line to theantenna without reflection back into the transmission line. Theremainder of the antenna is elliptically tapered to a much smallerdiameter at the free end of the radiator.

While throughout the present specification I have particularly referredto the antenna as a radiator, it is to be clearly understood that theantenna may equally well be used forreceiving signals and in thisservice the same results are obtained as in the transmission of signals.

The present invention will be more fully understood by reference to thefollowing detailed description, which is accompanied by drawings inwhich Figure 1 illustrates the ideal form of an antenna embodying theprinciples of the present invention, while Figure 2 illustrates amodification of the form shown in Figure 1, which is more easilyconstructed; Figures 3 and 4 illustrate by means of curves thepercentage of reflection obtained in antennas constructed according toFigures 1 and 2 with variation in the wavelength of energy appliedthereto; Figure 5 illustrates the horizontal directivity patternobtained by using a single radiator as shown in Figures 1 and 2, whileFigure 6 illustrates, in plan view, an antenna having a directivitycharacteristic with only a single major lobe.

Referring, now, to Figure 1, reference numeral N] indicates, generally,the radiator constructed according to the principles of my invention.The radiator in may consist of a plurality of separate conductors llconnected at one end to a small metallic cone l2 and at the other end tothe inner conductor I3 of transmission line TL. The transmission'line TLis connected to a conventional source of high frequency ener y, notshown. The radiator I0 has a maximum diameter at l5 of the order of onewavelength at midband frequency. The diameter may vary from .6 of awavelength up to one wavelength without a substantial variation incharacteristics. The region of maximum diameter should preferably bespaced from the transmission line end of the antenna, a distance ofapproximately one wavelength at the midband frequency. From the regionof maximum diameter the conductor tapers toward the far end where it isterminated by a small conductive cone. Preferably, the taper should beelliptical rather than purely conical. However, if the taper consists ofa series of short conical sections the form approximates the idealelliptical taper closely enough for all practical purposes. The firstportion of the antenna between the region of maximum diameter and thetransmission line should also be tapered in an elliptical manner so asto obtain as smooth a transition as possible between the impedance ofthe transmission line and the impedance of the antenna. The shaping ofthis portion of the antenna is far more critical than that of the otherportion of the antenna and has an import ant influence on reflection atthe input end.

The transmission line TL .preferably has its outer conductor [4 flaredout around the expanding portion of conductor l3 where it connects tothe radiator ll so as to aid in obtaining a smooth impedancetransformation, according to the principles set forth in my priorapplication #208,573, filed May is, 1938, now Patent No.

2,239,724. The extreme end of the outer conductor l4 may be connected toa ground sheet as shown or other convenient means such as the quarterwave trap disclosed in my prior application #183,571, filed January 6,1938, now Patent No. 2,238,904, may be employed to prevent highfrequency energy from flowing over the outer surface of the conductor M.

The antenna shown in Figure 2 follows, generally, the principles setforth above with reference to Figure 1. However, the construction issomewhat more easily accomplished since the taper from the region 25 ofthe maximum diameter to the minimum diameter regions is.

conic in form, the conductor wires being maintained in their properrelative relationship one to the other by means of spacing rings 25.Likewise, the first portion of the expansion of the radiator betweentransmission line TL and the portion of maximum diameter 25 is, insteadof being continuously tapered, tapered in steps. The steps should,however, be sufficiently closely spaced so as to obtain an approximationof an elliptic expansion.

Figure 3 is a curve in which is shown percentage reflection back intothe transmission line plotted against radiator length measured in wavemultiples. The relationships shown were obtained by utilizing a fixedlength antenna and varying the frequency applied to the antenna. Thecurve represents the results obtained with a radiator of a length equalto about 8 wavelengths at the middle frequency. It will be seen thatwithin the limits of 7 to 10 wavelengths the percentage of reflectionwas maintained below 20 percent.

Figure 4 shows a curve similar to that shown in Figure 3 wherein theantenna length is a greater multiple of the operating wavelength. Theantenna length in this case is about 11 wavelengths at the midbandfrequency. As may readily be seen the longer radiator achieves thedesired results much more efiectively. Over the entire range from 7 /2to 14 wavelengths a maximum reflection of only 14 percent isencountered, and it will further be evident that much lower reflectionis encountered over the major portions of this range. For example,between 8 and 12 wavelengths the reflection does not rise above 10percent.

Figure shows the directivity obtained with an antenna of the form shownin Figures 1 and 2. It will be noted that this directivity pattern showstwo maximum lobes one'at each side of the antenna axis. The pattern isnot entirely symmetrical due to the presence of unavoidable conductiveobjects within the field of the radiator tested. This pattern issomewhat similar to that obtained by the conventional long wire antenna.

A directivity pattern having only a single maximum lobe may be obtainedin the same way as that with previously known traveling wave antennas.One way in which this may be done is shown in Figure 6 wherein a pair ofradiators and 36 are disposed at an angle to one another, the b-isectorof the angle being in the direction of the maximum desired radiation.The magnitude of the angle is determined by the angle between the twomaximum lobes shown in Figure 5. The two radiators 35 and 3b are sodisposed the right-hand maximum lobe of the left-hand antenna and theleft-hand maximum directivity lobe of the right-hand antenna add to forma single large lobe in the desired direction while the other lobes arecorrespondingly reduced. The two antennas 35 and 36 are energized in thedesired phase relationship from any desired energy source by means oftransmission lines TL.

While I have particularly shown and described several modificationsofthe present invention, it is to be distinctly understood that myinvention is not limited to these particular embodiments but thatmodifications and alterations within the scope of the invention may bemade.

I claim:

1. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any frequencywithin said band, said conductor having a maximum transverse dimensionof the order of one wavelength near one end, means for energizing saidconductor at said one end, said conductor gradually tapering to a smalltransverse dimension at said other end.

2. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several. wavelengths of any frequencywithin said band, said conductor having a maximum transverse dimensiongreater than one-half wavelength near one end, means for energizing saidconductor at said one end, said conductor gradually tapering to a smalltransverse dimension at said other end.

3. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any frequencywithin said band, said conductor having a length equal to at leastseveral wavelengths of any frequency within said band, said conductorhaving a maximum transverse dimension of the order of one wavelengthnear one end, means for energizing said conductor at said one end, saidconductor gradually tapering to a small transverse dimension at saidother end, and said conductor being sharply tapered from said maximumtransverse dimension at said one end.

4. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any fre quencywithin said band, said conductor having a maximum transverse dimensiongreater than one-half wavelength near one end, means 'for energizingsaid conductor at said one end, said conductor gradually tapering to asmall transverse dimension at said other end, and said conductor beingsharply tapered from said maximum transverse dimension at said one end.

5. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any frequencywithin said band, said conductor having a maximum transverse dimensionof the order of one wavelength near one end, means for energizing saidconductor at said one end, said conductor gradually tapering to a smalltransverse dimension at said other end, and said conductor being sharplytapered from said maximum transverse dimension at said one end, saidtapers being elliptical in form whereby a smooth change incharacteristic 'impedances is obtained.

6. A wide band traveling wave antenna comprising a radiating conductorhaving a length equal to at least several wavelengths of any frequencywithin said band, said conductor having a maximum transverse dimensiongreater than onehalf wavelength near one end, means forenergizing saidconductor at said one end, said conductor gradually tapering to a smalltransverse dimension at said other end, and said conductor being sharplytapered from said maximum transverse dimension at said one end and saidtapers being elliptical in form whereby a smooth change incharacteristic impedances is obtained.

'7. A wide band traveling wave antenna comprising a radiatingconductorhaving a length equal to at least several wavelengths of anyfrequency within said band-said conductor having a maximum transversedimension of the order of one wavelength a distance substantially equalto one wavelength at midband frequency from one end, means forenergizing said conductor at said one end, said conductor graduallytapering to a small transverse dimension at said other end, and saidconductor being sharply tapered from said maximum transverse dimensionat said one end, said tapers being elliptical in form whereby a smoothchange in characteristic impedances is obtained.

8. A wide band traveling wave antenna system comprising a radiatingconductor having a length equal to at least several wavelengths of anyfrequency Within said band, said conductor having a maximum transversedimension at a distance substantially equal to one wavelength at midbandfrequency from one end of the order of one wavelength, 3, transmissionline having an inner conductor and an outer shell for connecting saidantenna to a transducer, the inner conductor of said transmission linebeing connected to said conductor at said one end, said conductorsmoothly tapering from said maximum transverse dimension to the diameterof said inner conductor whereby energy is transferred along saidtapering portion without reflection.

9. A wide band traveling wave antenna system comprising a radiatingconductor having a length equal to at least several Wavelengths of anyfrequency within said band, said conductor having a maximum transversedimension at a distance substantially equal to one wavelength at midbandfrequency from one end of the order of one wavelength, a transmissionline having an inner conductor and an outer shell for connecting saidantenna to a transducer, the inner conductor of said transmission linebeing connected to said conductor at said one end, said conductorsmoothly tapering from said maximum'transverse dimension to the diameterof said inner conductor whereby energy is transferred along saidtapering portion without reflection, said outer shell being flared atits end and surrounding a portion of said taper.

10. A wide ban-:1 traveling wave antenna system comprising a radiatingconductor having a length equal to at least several wavelengths of anyfrequency within said band, said conductor having a maximum transversedimension at a distance substantially equal to one wavelength at midbandfrequency from one end of the order of one wavelength, a transmissionline having an inner conductor and an outer shell for connecting saidantenna to a transducer, the inner conductor of said transmission linebeing connected to said conductor at said one end, said conductorsmoothly tapering from said maximum transverse dimension to the diameterof said inner conductor whereby energy is transferred along saidtapering portion without a reflection, said outer shell being flared atits end and surrounding a portion of said taper, means surrounding saidouter shell for preventing the flow of energy along the outer surfacethereof, said radiating conductors being tapered from its region ofmaximum transverse dimension throughout its length to said other end.

11. A wide band traveling wave antenna system comprising a radiatingconductor having a length equal to at least several wavelengths of anyfrequency Within said band, said conductor having a maximum transversedimension at a distance substantially equal to one wavelength at midbandfrequency from one end of the order of one wavelength, a transmissionline having an inner conductor and an outer shell for connecting saidantenna to a transducer, the inner conductor of said transmission linebeing connected to said conductor at said one end, said conductorsmoothly tapering from said maximum transverse dimension to the diameterof said inner conductor whereby energy is transferred along saidtapering portion Without reflection, said outer shell being flared atits end and. surrounding a portion of said taper, means surrounding saidouter shell for preventing the flow of energy along the outer surfacethereof, said radiating conductors being tapered from its region ofmaximum transverse dimension through* out its length to said other end,said tapers being elliptical in form.

12. An antenna as set forth in cl-aim'8, wherein said radiatingconductor is comprised of a plurality of longitudinal Wires defining thesurface thereof, said wires being connected to met-allic end pieces andsupported in position along the length of said conductor by spacingrings.

13. An antenna as set forth in claim 9, Wherein said radiating conductoris comprised of a plurality of longitudinal wires defining the surfacethereof, said wires being connected to metallic end pieces and supportedin position along the length of said conductor by spacing rings.

14. An antenna as set forth in claim 10, Wherein said radiatingconductor is comprised of a plurality of longitudinal wires defining thesurface thereof, said wires being connected to metallic end pieces andsupported in position along the length of said conductor by spacingrings.

15. An antenna as set forth in claim 11, wherein said radiatingconductor is comprised of a plurality of longitudinal wires defining thesurface thereof, said wires being connected to metallic end pieces andsupported in position along the length of said (conductor by spacingrings.

16. An antenna array comprising a pair of antennae as set forth in claim3, lying in a common horizontal plane with their one ends adjacent andstorming an angle, the bisector of said angle being directed in thedesired direction of communication.

17. An antenna array comprising a pair of antennae as set forth in claim8, lying in a common horizontal plane with their one ends adjacent andforming an angle, the 'bisector of said angle being directed in thedesired direction of communication.

18. An antenna array comprising a pair of antennae as set forth in claim11, lying in a common horizontal plane with their one ends adjacent andforming an angle, the bisector of said.

angle being directed in the desired direction of communication.

NJLS E. LINDENBLAD.

